Pelletizing device and blade head and/or grinding head for such a pelletizing device

ABSTRACT

The present invention relates to a pelletizer, preferably in the form of an underwater pelletizer. In particular, this invention relates to a cutter and/or grinding head for such pelletizer, comprising a tool carrier which can rotatorily be driven about a tool carrier axis of rotation, and at least one cutting and/or grinding tool, which is attached to the tool carrier and is spaced from the tool carrier axis of rotation, for knocking off plastic melt emerging from a pelletizer die plate and/or for grinding said pelletizer die plate. In accordance with the invention, the cutting and/or grinding tool is rotatably mounted on the tool carrier about an axis of rotation spaced from the tool carrier axis of rotation. This provides a second component of movement for the cutting and/or grinding tool. On the one hand, the cutting and/or grinding tool rotates together with the tool carrier about its tool carrier axis of rotation, and on the other hand, the cutting and/or grinding tool can rotate about its own axis of rotation relative to the tool carrier. The tool carrier has a pivot bearing for the cutting and/or grinding tool, by means of which the cutting and/or grinding tool can rotate about itself.

The present invention relates to a pelletizer preferably in the form of an underwater pelletizer. In particular, the invention relates to a cutter and/or grinding head for such pelletizer, comprising a tool carrier which can rotatorily be driven about a tool carrier axis of rotation, and at least one cutting and/or grinding tool, which is attached to the tool carrier and is spaced from the tool carrier axis of rotation, for knocking off plastic melt emerging from a pelletizer die plate and/or for grinding said pelletizer die plate.

Pelletizers for instance in the form of underwater pelletizers usually have a pelletizer die plate with a plurality of bores or channels, through which plastic melt is pressed in the form of a strand. On the outlet side, the emerging strands of plastic melt are knocked or cut off by a rotating cutter head, so that plastic pellets are obtained, which in the case of an underwater pelletizer are carried away by the process fluid flowing around the cutting head.

The quality of the plastic pellets and of the pelletizing process depends for instance on the shape and surface accuracy of the die plate on its outlet side and on the precise geometrical interaction between the outlet side of the die plate and the cutting or knock-off tools passing over the same. If wear results for instance in irregularities on the die plate outlet side, the plastic material can start to smear on the die plate outlet side, whereby neatly cutting or knocking off the pellets is impaired. Therefore, it has already been proposed to surface-grind the die plate of the pelletizer from time to time and instead of the cutter head use a grinding head with an end-face abrasive coat, which is urged against the outlet side of the die plate, in order to surface-grind the latter. However, restrictions are placed on the surface accuracy and fineness to be achieved here, and in particular due to the usual uniaxial rotatory grinding movement annular rigdes can be cut into the die plate surface.

Beside the wear on the die plate, wear on the cutting tools also can impair the pelletizing process. Usually, cutting plates are used as cutting tools, which can be mounted in cutting plate holders at the desired angle, so that they can pass over the die plate in the specified angular position, in order to knock off the emerging melt. It is known here to use turnover plates, i.e. said cutting plates can be turned over in the cutting plate holders, so that both sides so to speak of the usually rectangular cutting plates can be used, until they must be discarded due to excessive wear. The stability of the cutting plates is, however, limited here, and when changing the cutting surface, differences in shape with respect to the ground outlet side of the die plate sometimes are obtained.

This problem should be solved with the present invention. It is the object underlying the invention to create an improved pelletizing device and an improved cutter and/or grinding head for a pelletizer, which avoid the disadvantages of the prior art and develop the latter in an advantageous way. In particular, an improved tool head should be created, which equally allows both grinding the outlet side of the die plate of the pelletizer and cutting or knocking off the plastic melt emerging from the die plate and has an improved service life with more favorable wear properties of the working tool.

In accordance with the invention, this object is solved by a cutting and/or grinding head according to claim 1 and a pelletizer according to claim 21. Preferred aspects of the invention are subject-matter of the dependent claims.

Thus, it is proposed to attach the at least one cutting and/or grinding tool to the tool carrier not rigidly in a specified position, but to provide the same with an additional degree of freedom or an additional axis of movement with respect to the tool carrier, so that the cutting and/or grinding tool can move with respect to the tool carrier. In accordance with the invention, the cutting and/or grinding tool is rotatably mounted on the tool carrier about an axis of rotation spaced from the tool carrier axis of rotation. This provides a second component of movement for the cutting and/or grinding tool. On the one hand, the cutting and/or grinding tool rotates together with the tool carrier about its tool carrier axis of rotation, and on the other hand, the cutting and/or grinding tool can rotate about its own axis of rotation relative to the tool carrier. The tool carrier has a pivot bearing for the cutting and/or grinding tool, by means of which the cutting and/or grinding tool can rotate about itself.

Due to the additional component of movement of the cutting and/or grinding tool, the wear of said cutting and/or grinding tool itself on the one hand can be rendered more uniform, as different portions are worn depending on the rotary position, which in the course of time adds up to a uniform wear. On the other hand, especially in the grinding process, when the grinding and/or cutting tool is used for grinding, the superimposed component of movement can prevent the formation of annular ridges around the tool carrier axis of rotation. On the outlet side of the die plate, a much finer surface of greater shape accuracy is achieved. Furthermore, the rotary movement of the grinding and/or cutting tool about itself can also be utilized for a better removal of the pellets knocked off, and for cutting or knocking off the next strand of plastic melt a fresh portion of the tool is available, so to speak.

The axis of rotation of the at least one cutting and/or grinding tool advantageously extends substantially parallel to the tool carrier axis of rotation. The axis of rotation possibly could also be slightly inclined with respect to the tool carrier axis of rotation, which possibly can be advantageous for generating the rotary movement of the cutting and/or grinding tool. What is preferred, however, is a parallel arrangement of the axis of rotation of the cutting and/or grinding tool with respect to the tool carrier axis of rotation.

In accordance with a development of the invention, the axis of rotation of the cutting and/or grinding tool is aligned on the tool carrier directionally stable. Alternatively, the axis of rotation of the cutting and/or grinding tool also can be arranged or mounted so as to be tiltable to a limited extent, in order to achieve a self-adjustment of the cutting and/or grinding tool or to compensate minor alignment errors. The cutting and/or grinding tool can be self-adjusting, so to speak, so that it can slightly tilt with respect to the tool carrier. To achieve a simple, stable mounting, the directionally stable mounting of the axis of rotation on the tool carrier as described above, however, is preferred.

In accordance with an advantageous development of the invention, the cutting and/or grinding tool is mounted on the tool carrier free from a rotatory drive or freely self-rotating. In operation of the cutter and/or grinding head, the cutting and/or grinding tool remains rotatable, wherein the desired rotary movement is obtained by the cooperation of the cutting and/or grinding tool with the die plate, in particular by the different peripheral speeds of different portions of the cutting and/or grinding tool relative to the die plate. When the cutting and/or grinding tool passes around the tool carrier axis of rotation on a circular path as a result of the rotation of the tool carrier, a portion of the cutting and/or grinding tool located radially further on the outside has a greater peripheral speed than a portion located further on the inside. This difference leads to a rotation of the cutting and/or grinding tool during operation about its own axis of rotation. As an alternative to such drive-free mounting and self-rotating configuration of the cutting and/or grinding tools, a drive for the forced driving of the cutting and/or grinding tool relative to the tool carrier might be provided, for instance in the form of an intermediate transmission, which derives the corresponding rotary movement of the cutting and/or grinding tool from the rotary movement of the tool carrier. In this way, higher relative speeds can be achieved between tool and die plate surface. What is preferred, however, is the above-described drive-free and self-rotating configuration of the cutting and/or grinding tool, as a certain irregularity in the rotary speed can provide advantages with respect to an accurately ground die plate surface.

In accordance with a development of the invention, the axis of rotation of the cutting and/or grinding tool is arranged at a fixed distance from the tool carrier axis of rotation, wherein said distance advantageously is chosen such that the cutting and/or grinding tool passes over the pelletizer die plate in the vicinity of at least one associated outlet bore or outlet duct.

In accordance with an alternative embodiment of the invention, an adjusting device for the distance of the axis of rotation of the cutting and/or grinding tool can, however, also be provided, so that the distance of the axis of rotation of the cutting and/or grinding tool from the tool carrier axis of rotation is adjustable. As a result, the cutter or grinding head can be used for different pelletizer die plates. When using for instance a pelletizer die plate with a larger hole center distance, the cutting and/or grinding tool merely is moved further to the outside on the tool carrier, i.e. moved further away from the tool carrier axis of rotation, so that it is adapted to the corresponding geometry of the pelletizer die plate.

In principle, the adjusting device for the distance of the axis of rotation of the cutting and/or grinding tool can be formed differently. For instance, the tool carrier can include a slotted longitudinal guideway for instance in the form of an oblong-hole guideway in which the cutting and/or grinding tool can be moved, in order to adjust the distance from the tool carrier axis of rotation. In accordance with a preferred development of the invention, the adjusting device also can include a swivel arm, which on the one hand is pivotally attached to the body of the tool carrier and on the other hand carries the cutting and/or grinding tool and its axis of rotation. When the swivel arm is swivelled further to the outside, the distance of the cutting and/or grinding tool mounted thereon from the tool carrier axis of rotation is increasing. On the other hand, said distance can be reduced by swivelling said swivel arm to the inside.

Advantageously, a fixing device is associated to the adjusting device, by means of which at least two different distances of the tool axis of rotation from the tool carrier axis of rotation can be fixed. The fixing device can include for instance a positive locking device and/or a clamping device, for instance in the form of a clamping screw bolt.

In principle, the at least one rotatably mounted cutting and/or grinding tool can have different geometries and configurations. In accordance with a development of the invention, the cutting and/or grinding tool can have a substantially planar end face for bearing against the pelletizer die plate, wherein the planar end face does not need to extend over the entire cross-section of the working head of the cutting and/or grinding tool. For instance, the working head of the cutting and/or grinding tool can also have an annular end face and a concave recess in the center of the end face, so that merely said annular surface bears against the die plate, wherein advantageously at least said annular end face is formed flat and extends in a plane vertical to the axis of rotation of the tool.

For surface grinding the pelletizer die plate, the end face of said cutting and/or grinding tool can be provided with an abrasive coat and/or an abrasive structure. For instance, an abrasive coat can be applied in the form of a diamond grain carpet on the end face of the cutting and/or grinding tool. Alternatively or in addition, the end face of the cutting and/or grinding tool can also be provided with a microstructure incorporated in the material of the working head, for instance in the form of fishscales with corresponding cutting or grinding edges, which provide for a machining, abrasive removal of material on the die plate. Alternatively or in addition, a grinding fluid or emulsion containing abrasive grains can also be applied onto the die plate or between die plate and grinding head, in order to achieve an abrasive effect possibly also without an abrasive coat on the end face of the working head.

To be able to selectively also operate only as a cutting tool for knocking off the strands of plastic melt, said abrasive coat can releasably be connectable with the end face of the tool working head, for instance be clampable onto a backing pad in the manner of a grinding wheel. Alternatively or in addition, the cutting and/or grinding tool can releasably and replaceably be mounted on the tool carrier, so that a grinding tool with abrasive coat and a cutting tool without abrasive coat can selectively be mounted on the tool carrier. Independent of the exchangeability of different types of tool, the replaceability of the cutting and/or grinding tool on the tool carrier is advantageous, in order to avoid that the entire cutting or grinding head must be replaced in the case of wear.

Depending on the plastic melt to be pelletized, different configurations and geometries of the cutting and/or grinding tool can be advantageous. In particular, differently formed cutting or knock-off edges can be used, in order to pelletize the emerging strands of plastic melt in the desired way. An advantageous embodiment of the invention can consist in that the cutting and/or grinding tool is formed symmetrical with respect to its axis of rotation and/or has segments which can be made to coincide by rotation about said axis of rotation, so that there is no continuous rotation symmetry, so to speak, but a symmetry upon rotation about a predetermined angular amount. The tool can have a pitch and be divided into segments, which can be made to coincide by rotating the same by the corresponding pitch angle.

In particular, the cutting and/or grinding tool can have a rotationally symmetric working head with circular cross-section in accordance with a preferred development of the invention, so that the cutting and/or grinding tool can rotate and wear completely uniformly. It has a working edge uniform over 360° C., so to speak, for knocking or cutting off the plastic strands during pelletizing.

Alternatively, however, the working head can also have a cross-section different from the circular shape, in particular in the form of a peripheral contour with pitch-symmetrically identically shaped segments, as mentioned above. When providing a plurality of congruent peripheral segments, different working head geometries can be chosen in principle. For instance, the working head can have a generally blossom- and/or flower-shaped contour which is divided into a plurality of arcuate peripheral segments. Alternatively or in addition, the working head of the cutting and/or grinding tool also can have a polygonally profiled contour with preferably rounded transitions between the polygon portions. For example, a substantially polygonal, for instance hexagonal or octagonal working head with rounded transitions between the segments can be provided.

To achieve that the plastic strands emerging from the melt ducts of the die plate are neatly pelletized, the cutting and/or grinding tool has a peripheral flank constituting a cutting and/or knock-off edge in accordance with a development of the invention. Said cutting and/or knock-off edge advantageously extends around the axis of rotation, and in particular with a circular cross-section of the working head, it can form an annular flank, which defines a cutting or knock-off edge extending over 360°. Alternatively, a segmental configuration of said cutting and/or knock-off edge can be provided, which in terms of a pitch angle advantageously is congruent, for instance in the above-mentioned blossom shape or traverse shape with rounded transitions, so that for instance cutting and/or knock-off edge segments are provided, which extend over six times 60°.

Depending on the plastic melt to be cut, different angles of inclination of the peripheral flank or of the cutting and/or knock-off edge formed by the same can be advantageous. In accordance with a development of the invention, the peripheral flank includes a flank angle in the range from 110° to 30° with respect to an end plane of the working head vertical to the axis of rotation, and in accordance with a preferred development of the invention, said flank angle can lie in the range from 90° to 45°, in particular about 90° to 75°.

As viewed in a longitudinal section including the axis of rotation of the tool, the peripheral flank can have different shapes, for instance be formed convex or also concave. Depending on its configuration, such curved shape of the flank can effect a sharper separation of the melt strands or a more impulsive knocking off. In accordance with a preferred development of the invention, however, the peripheral flank as viewed in a longitudinal section including the axis of rotation of the tool has a straight flank, which can be inclined in the aforementioned flank angle with respect to the vertical end plane.

The invention will subsequently be explained in detail with reference to preferred embodiments and associated drawings, in which:

FIG. 1: shows a schematic, perspective representation of a cutting and grinding head of an underwater pelletizer on the pelletizer die plate in accordance with an advantageous embodiment of the invention,

FIG. 2: shows a schematic representation of the cutting and grinding head of the underwater pelletizer of FIG. 1, wherein the cutting and grinding head is shown in the partial views A, B and C in a top view, in a side view, and in a perspective view,

FIG. 3: shows a schematic representation of the cutting and grinding head of the pelletizer of FIG. 1 in accordance with a further embodiment of the invention, in which the cutting and knock-off flank of the cutting and grinding tools has a flank angle of 75°, wherein the cutting and grinding head is shown in views A, B, C in a top view, in a side view, and in a perspective view,

FIG. 4: shows a schematic representation of the cutting and grinding head of the pelletizer of FIG. 1 in accordance with a further embodiment of the invention, in which the cutting and knock-off flank of the cutting and grinding tools has a flank angle of 90°, wherein the cutting and grinding head is shown in views A, B, C in a top view, in a side view, and in a perspective view,

FIG. 5: shows a schematic side view of the rotatably mounted cutting and grinding tool of the cutting and grinding heads of the preceding Figures, wherein views A, B, C and D show different tool geometries,

FIG. 6: shows an end-face top view of a cutting and grinding tool of the cutting and grinding head of the preceding Figures, wherein the different views A to E show various possible peripheral contours of the working head of the cutting and grinding tool, and

FIG. 7: shows a perspective view of a cutting and grinding head of an underwater pelletizer in a further advantageous embodiment of the invention, according to which the tool carrier includes an adjusting device in the form of swivel arms for adjusting the distance of the axes of rotation of the cutting and grinding tools from the tool carrier axis of rotation.

In the embodiment illustrated in FIG. 1, the only partly represented pelletizing device 1 includes a cutting and grinding head 2, which comprises a substantially plate-like, ring-shaped tool carrier 3. Said tool carrier 3 can rotatorily be driven about a tool carrier axis of rotation 4 by a non-illustrated drive shaft. In the illustrated embodiment 1, the tool carrier 3 comprises a central, hub-like recess 5, by means of which the tool carrier 3 can be mounted on said drive shaft or on a cutting and grinding head bearing provided thereon.

As shown in FIGS. 1 to 4, the tool carrier 3 carries a plurality of cutting and grinding tools 6 spaced from its tool carrier axis of rotation 4, which are arranged on the end face of the tool carrier 3 and axially protrude beyond the body of said tool carrier 3. Advantageously, between two and ten, preferably between two and six cutting and grinding tools 6 are provided. In the illustrated embodiment, four of such cutting and grinding tools 6 advantageously are attached to the tool carrier 3. The cutting and grinding tools 6 can be formed differently. Advantageously, however, identically formed cutting and grinding tools are attached to the tool carrier 3.

In accordance with the embodiments illustrated in FIGS. 1 to 4, the cutting and grinding tool 6 comprises a rotationally symmetric, approximately plate-shaped working head 7, which in the illustrated embodiments as shown in FIGS. 1 to 4 has a circular cross-section. Said cutting and grinding tools 6 each are rotatably mounted on the tool carrier 3. The pivot bearings 8 provided for this purpose advantageously each have an axis of rotation 9, which extends substantially parallel to the central tool carrier axis of rotation. The pivot bearings 8 advantageously are recessed or integrated in the body of the tool carrier 3.

As shown in FIG. 5, the cutting and grinding tools 6 can include a bearing portion 10 molded to the working head 7, which can have the shape of a bearing pin or another suitable form of bearing member. In general, the cutting and/or grinding tool 6 thereby obtains a generally approximately mushroom-like configuration.

Said cutting and grinding tools 6 are freely rotatable on the tool carrier 3 by means of the pivot bearings 8. Although they are mounted on the tool carrier 3 free from drive, they nevertheless perform a rotary movement in operation. As shown in FIG. 1, the cutting and grinding tools 6 are spaced from the tool carrier axis of rotation 4 such that they approximately come to lie on the melt passages 11 of the pelletizer die plate 12 or on the outlets thereof. In the illustrated embodiment as shown in FIG. 1, the melt passages 11 in the pelletizer die plate 12 are arranged on a hole circle or arranged in an annular portion, which slightly protrudes with respect to the remaining body of the pelletizer die plate 12 and forms a flat end face of the pelletizer die plate 12, cf. FIG. 1.

The substantially flat end face of the cutting and grinding tools 6 is seated on said ring portion 13 of the pelletizer die plate 12. When rotating together with the tool carrier 3 about its tool carrier axis of rotation 4, they undergo different peripheral speeds in different portions, which effects a self-rotation of said cutting and grinding tools 6 about their axes of rotation 9. Said cutting and grinding tools 6 thus perform two superimposed rotary movements, namely on the one hand the rotary movement about the tool carrier axis of rotation 4 and on the other hand the superimposed self-rotation about the axes of rotation 9.

As shown more clearly in FIG. 5, the working heads 7 of the cutting and grinding tools 6 have a flat end face 14, which possibly can be ring-shaped, as is shown in FIG. 5C. Said end face 14 is surrounded by an annular peripheral flank 15, which forms a cutting or knock-off edge for cutting off or separating the strands of plastic melt emerging from the melt passages 11. In principle, the working head 7 can have a substantially cylindrical contour, as is also shown in FIG. 4 beside FIGS. 5B, 5C and 5D. In this case, said peripheral flank 15 is inclined under an angle of 90° with respect to an end-face plane of the respective working head 7, which is vertical to the axis of rotation 9, cf. FIG. 4B.

Alternatively, the working head 7 can also be conical, so that its peripheral flank 15 is inclined under an acute angle with respect to said end-face plane. FIG. 2 shows a conically formed working head 7 with a flank angle of about 45°, whereas the embodiment of FIG. 3 shows a conical working head with a flank angle of about 75°. The smaller said flank angle 16, the sharper the melt strands are cut through, whereas with a more vertical peripheral flank they are knocked off impulsively.

The height of the working head 7 of the cutting and grinding tools 6, as measured in the direction of the axis of rotation 9, can be adapted to the different plastic melts to be pelletized and can vary. In accordance with a preferred development of the invention, the height 17, cf. FIG. 5D, of the working head 7 will be smaller than the diameter of the working head 7, wherein the height 17 preferably is less than half the diameter, in particular less than one third of the diameter of the working head 7. For instance, the height 17 can lie in the range from about one tenth to one third of the diameter of the working head 7.

The diameter of the working head 7 of the cutting and grinding tools 6 likewise can be adapted to the different pelletizing conditions and in particular to the geometry of the pelletizer die plate 12. In accordance with an advantageous embodiment, the working head diameter can be about 10% to 150%, preferably about 30% to 100%, in particular about 50% to 75% of the distance of the axes of rotation 9 from the central tool carrier axis of rotation 4. In principle, the axes of rotation 9 of the cutting and grinding tools 6 can be arranged at different distances from the central tool carrier axis of rotation 4, in particular when the pelletizer die plate 12 includes more than one melt passage circle. In accordance with the illustrated embodiment, however, the cutting and grinding tools 6 advantageously can all be arranged at the same distance from the central tool carrier axis of rotation 4.

FIG. 7 shows another advantageous embodiment of the invention, according to which the tool carrier 3 is adjustable with respect to the distance of the axis of rotation 9 of the cutting and grinding tools 6 from the central tool carrier axis of rotation 4. In the illustrated embodiment, the corresponding adjusting device 18 comprises swivel arms 19, one end of which is pivotally attached to the body of the tool carrier 3, namely about swivel axes which extend parallel to the central tool carrier axis of rotation 4. On their other protruding end, said swivel arms 19 carry the cutting and grinding tools 6 together with their axes of rotation 9 and the associated pivot bearings 8. When the swivel arms 19 are swivelled further to the outside, the distance of the cutting and grinding tools 6 from the tool carrier axis of rotation 4 will increase, and on the other hand, this distance can be reduced by swivelling the swivel arms 19 to the inside. The cutting and grinding tools 6 advantageously can be adjusted individually, so that possibly different distances can also be adjusted for different cutting and grinding tools 6, for instance such that every second cutting and grinding tool 6 is running further on the outside than every third cutting and grinding tool. The adjusting device 18 comprises fixing means for fixing the respectively desired position. In the illustrated embodiment, clamping bolts are provided as fixing means 20 for clamping the swivel arms 19 in the respective swivel position.

As shown in FIG. 6, the working head 7 can have different cross-sections, for instance a circular cross-section in accordance with an advantageous development of the invention, cf. FIG. 6A. Alternatively, blossom- or flower-shaped peripheral contours can be specified, cf. FIGS. 6B and 6E. As a further alternative, polygonal peripheral profiles preferably with rounded transitions are possible, cf. FIGS. 6C and 6E. 

1-21. (canceled)
 22. A cutter and/or grinding head for a pelletizer, preferably underwater pelletizer (1), said head comprising a tool carrier (3) to be driven rotatorily about a tool carrier axis of rotation (4), and at least one cutting and/or grinding tool (6) for knocking off plastic melt emerging from a pelletizer die plate (12) and/or for grinding said pelletizer die plate (12), wherein said cutting and/or grinding tool (6) is rotatably mounted on said tool carrier (3) about an axis of rotation (9) spaced from the tool carrier axis of rotation (4), wherein said axis of rotation (9) of said cutting and/or grinding tool (6) extends substantially parallel to the tool carrier axis of rotation (4), wherein said cutting and/or grinding tool (6) includes a substantially planar end face (14) extending perpendicular to said axis of rotation (9), for bearing against the pelletizer die plate (12), wherein the said end face (14) is adapted to be provided with an abrasive coat (21) and/or an abrasive structure, and wherein said cutting and/or grinding tool (6) is rotatably supported on said tool carrier (3) free from a rotatory drive in a freely self-rotating manner.
 23. The cutter and/or grinding head according to claim 22, wherein the tool carrier (3) includes an adjusting device (18) for adjusting the distance of the axis of rotation (9) of the cutting and/or grinding tool (6) from the tool carrier axis of rotation (4).
 24. The cutter and/or grinding head according to the preceding claim, wherein the adjusting device (18) includes a swivel arm (19), which on the one hand is pivotally mounted on the body of the tool carrier (3) and on the other hand carries the cutting and/or grinding tool (6) together with its axis of rotation (9).
 25. The cutter and/or grinding head according to the preceding claim, wherein fixing means (20) are provided for fixing the swivel arm (19) in at least two different swivel positions relative to the body of the tool carrier (3).
 26. The cutter and/or grinding head according to claim 22, wherein the cutting and/or grinding tool (6) is formed symmetrical with respect to its axis of rotation (9) and/or includes a plurality of segments, which can congruently be transferred into each other by rotating about the axis of rotation (9).
 27. The cutter and/or grinding head according to claim 22, wherein the cutting and/or grinding tool (6) includes a rotationally symmetric working head (7) with circular cross-section.
 28. The cutter and/or grinding head according to claim 22, wherein the cutting and/or grinding tool (6) includes a working head (7) with a cross-section differing from the circular shape, wherein the working head (7) is divided into a plurality of preferably congruent peripheral segments.
 29. The cutter and/or grinding head according to the preceding claim, wherein the working head (7) has a blossom- and/or flower-shaped contour with a plurality of arcuate peripheral segments.
 30. The cutter and/or grinding head according to claim 28, wherein the working head (7) has a traverse-shaped contour with preferably rounded transitions between the polygon portions.
 31. The cutter and/or grinding head according to claim 22, wherein the cutting and/or grinding tool (6) includes a peripheral flank (15) constituting a cutting and/or knock-off edge, wherein the cutting and/or knock-off edge is formed to extend around the axis of rotation (9).
 32. The cutter and/or grinding head according to the preceding claim, wherein the cutting and/or knock-off edge is formed rotationally symmetric with respect to the axis of rotation (9) and/or segmentally congruent with respect to the axis of rotation (9).
 33. The cutter and/or grinding head according to claim 22, wherein the peripheral flank (15) of the cutting and/or grinding tool (6) has a straight flank extension as viewed in a longitudinal section including the axis of rotation (9).
 34. The cutter and/or grinding head according to claim 22, wherein the peripheral flank (15) includes a flank angle (16) between 110° and 30°, preferably between 90° and 45°, in particular about 90° to 75°, with respect to an end plane vertical to the axis of rotation (9).
 35. The cutter and/or grinding head according to claim 22, wherein a plurality of cutting and/or grinding tools (6) are provided spaced from each other in peripheral direction around the axis of rotation (4).
 36. A pelletizer, in particular an underwater pelletizer (1), comprising a cutter and/or grinding head (2) according to claim 22, and a pelletizer die plate (12) with at least one melt passage (11), which is arranged in the vicinity of the path of circulation of the at least one cutting and/or grinding tool (6) of the cutter and/or grinding head (2). 